Check normal things. Chain, sprockets, tires, steering head, swing arm bearings, Wheel bearings, etc. A 280txt should have awesome compression and even be hard to kick over. A good 2 smoke should always start on the first or second kick. If you have to kick the shit out of it then it probably needs top end work. Check the frame for cracks and gouges. normal dings are OK on a trials bike and you will put some in yourself.

Hold the bike upright and push down on the foot peg. The front and back should go down at the same time if the suspension is set up right.

Make sure the clutch will release and also that it will grab. There are lots of plates in there and they get a bit snippy some times.